Citizen / General public
Researcher
Student / Future student
Company
Public partner
Journalist
Teacher / Pupil

Lower oceanic crust formed by in situ magma crystallization

While two-thirds of the Earth's crust is formed at ocean ridges by mantle melting, the process by which the lower part of the crust is formed is still debated. Using state-of-the-art analysis methods applied to seismic data from the Atlantic Ocean, researchers at IPGP and Australia's Commonwealth Scientific and Industrial Research Organisation have discovered different rock layers in the lower crust, suggesting that it is formed by cooling and crystallization of magma in situ.

Lower oceanic crust formed by in situ magma crystallization

Publication date: 16/06/2022

Press, Research

Related teams :
Marine Geosciences

Oceanic ridges form a chain of volcanoes in the middle of the oceans, stretching over 60,000 km around the Earth. As the oceanic plates move apart, the mantle rises, causing it to melt at a depth of around 70 km, and magma progresses towards the surface; some of this magma erupts onto the ocean floor while a large portion remains in the crust, probably in the form of magma lenses, and cools and then crystallizes to form the lower crust, scientists propose in a study published in Nature Geoscience, June 13th, 2022. The Moho (Mohorovičić discontinuity) is the boundary that separates this newly formed crust from the underlying mantle.

For this study, a team of researchers from the Institut de Physique du Globe de Paris (IPGP, Université Paris Cité, CNRS) and GEOMAR Helmholtz Centre for Ocean Research in Germany conducted an oceanographic campaign in the equatorial Atlantic Ocean in 2017 aboard the German oceanographic vessel Maria S. Merian. They deployed ocean bottom seismometers (OBS) on the seafloor to record the source of sound energy emitted by the ship and their propagation in the crust. The recorded signals were then analyzed on IPGP’s S-CAPAD supercomputing platform, using the full seismic waveform inversion method developed at the institute. This analysis revealed the presence of 400-500 m thick layers of different rock types starting 2 km below the seafloor. These results indicate that seawater penetrates 2-3 km below the seafloor, cooling the magma and circulating minerals and nutrients to the seafloor at hydrothermal sites (black smokers) feeding millions of living organisms in the ocean depths. The cooled magma then crystallizes on the spot, forming layers of rock of different compositions. These layers extend between 5 and 15 km along the profile studied, covering the crust that formed between 300 and 800 thousand years ago, suggesting that crustal accretion is a stable process.

Diagram illustrating the structure of oceanic crust at the Mid-Atlantic Ridge and far from the ridge axis. Black circles and bars represent basaltic lava and dikes. Thin blue ellipses represent hydrothermal alteration. Vertical ellipses in red represent magma upwelling in the mantle. The light-brown layers represent the different rock layers in the lower crust.
Ocean Bottom Seismometers (OBS) deployed during the 2017 oceanographic campaign.

The results of this study, funded by the European Research Council (ERC), suggest that oceanic crust at slow oceanic ridges is also essentially formed by magmatic action, similar to fast ridges, and that magma plays a fundamental role in the formation of oceanic crust.

Ref : Guo, P., Singh, S.C., Vaddineni, V., Grevemeyer, I., and Saygin, E. Lower oceanic crust formed by in situ melt crystallization revealed by seismic layering, Nature Geoscience, 15, https://doi.org/10.1038/s41561-022-00963-w

Latest news
A new tectonic micro-plate identified north of the Dead Sea Fault
A new tectonic micro-plate identified north of the Dead Sea Fault
In a study published in Science Advances, an international team has systematically analysed Sentinels-2 radar images to identify a new tectonic micro-...
Yann Klinger awarded ERC Advanced Grant 2023
Yann Klinger awarded ERC Advanced Grant 2023
Yann Klinger, CNRS Research Director and head of the Tectonics and Mechanics of the Lithosphere team at the IPGP, has been awarded the prestigious Eur...
Meteorites and magnetism in comics!
Meteorites and magnetism in comics!
To make it easier to communicate her research subject, a researcher from the IPGP and MIT has teamed up with an illustrator, herself a geophysicist, t...
The NanoMagSat mission gets go-ahead from ESA!
The NanoMagSat mission gets go-ahead from ESA!
The Programme Board for Earth Observation of the European Space Agency (ESA) has just decided to proceed with the NanoMagSat mission. This mission, in...